The invention relates to a condensation dryer comprising a drying chamber for the articles to be dried, a process air circuit in which a heater for heating the process air is located and wherein the heated process air can be guided across the articles to be dried by means of a blower, an air/air heat exchanger and a heat pump circuit comprising an evaporator, a compressor and a condenser, and a method for operating same.
Tumble dryers, whose mode of operation is based on the condensation of the moisture evaporated from the washing by means of warm process air from the process air discharged from the washing—so-called condensation dryers—do not require a hose for discharging the process air charged with moisture and are very popular because they can be used in internal bathrooms or utility rooms of larger housing complexes. This applies both to tumble dryers intended specifically for drying washing and also to so-called washer dryers, that is to say appliances which are able to both wash and also dry washing. Each and any subsequent reference to a “tumble dryers” or “condensation dryer” therefore applies both to an appliance intended only for drying and also to an appliance intended equally for washing and drying.
In a condensation dryer, air (so-called process air) is directed by a blower by way of a heater into a drum containing moist items of washing as a drying chamber. The hot air takes up moisture from the items of washing to be dried. After passing through the drum, the now moist process air is directed into a heat exchanger, which usually has a lint filter connected upstream.
In the heat exchanger the moist process air is cooled, for example by means of a separately guided cooling air current, such that the moisture contained in the process air condenses as water. The condensed water is then as a general rule collected in a suitable container for subsequent disposal and the cooled and dried air is delivered again to the heater and then to the drum.
This drying operation is energy intensive because the heat extracted during the cooling of the process air in the heat exchanger is lost to the process in terms of energy efficiency, in any case in the situation when this heat is discharged in a cooling air current. This loss of energy can be significantly reduced through the use of a heat pump. In the case of a condensation dryer equipped with a heat pump the cooling of the warm process air charged with moisture takes place essentially in a first heat exchanger of the heat pump, in particular an evaporator, where the transferred heat is used in order to evaporate a cooling agent employed in the heat pump. Such cooling agent evaporated as a result of the heating is delivered by way of a compressor to a second heat exchanger, in the given case and subsequently also referred to as “condenser”, of the heat pump, where as a result of the condensation of the gaseous cooling agent heat is released which in turn is used for heating the process air prior to its entry into the drum. The liquefied cooling agent passes through a control valve, which reduces its pressure, back to the evaporator in order to evaporate there whilst taking up heat again from the process air.
A tumble dryers comprising a heat pump is described in DE 40 23 000 C2, in which tumble dryer an inlet air opening which can be closed by means of a controllable closure device is arranged in the process air duct between the condenser and the evaporator.
A condensation dryer comprising a closed process air circuit is described in DE 197 38 735 C2, which condensation dryer is equipped with a heat pump. The heat pump is designed as a device operating in accordance with the absorber principle, the absorber of which device forms a third heat exchanger whose primary circuit has cooling agent flowing through it, and through whose secondary circuit the process air flowing away from the second heat exchanger is fed once again to the secondary circuit of the first heat exchanger.
The air/air heat exchanger customarily used—operated in crossing mode or in opposite stream mode—and the electrical heater are in general replaced completely by a heat pump. By this means, improvements in energy performance of 20 to 50% can be achieved.
Compressor units as described above are used as popular heat pumps. As a rule these operate optimally in a particular temperature range. Problematical regarding the use of a compressor heat pump in the condensation dryer are the mostly high temperatures in the condenser which for process-related reasons result in the fact that the compressor needs to be switched off and/or that the level of efficiency of the heat pump deteriorates. This problem is all the worse if the compressor is supported by an additional heater in the process air circuit in order to achieve a faster and/or greater heating of the process air and thus shorter drying times. A means for monitoring and/or reducing the cooling agent temperatures in the heat pump circuit is therefore desirable.
In order to eliminate this problem, the compressor can for example be cooled by means of an additional fan. Furthermore, the cooling agent can be additionally cooled after the condenser by using an additional heat exchanger which is equipped with an additional blower. These solutions have the disadvantage that additional resource deployment, in particular an additional blower, is required.